When a semiconductor device such as a metal-oxide-semiconductor field-effect transistors (MOSFETs) is scaled down through various technology nodes, high-k dielectric material and metal gate are adopted to form a gate stack. Strained structures utilizing epitaxy silicon germanium (SiGe) and silicon carbon (SiC) films may be used to enhance carrier mobility. In addition, channel-last integration schemes may also become a requirement for low melting temperature III-V high mobility channel materials such as InAs and InSb to avoid impact from high thermal budget associated with source/drain formation. However, current techniques to form these strained structures and channel-last transistors have not been satisfactory in all respects. For example, Si N-channel strain is limited to problematic SiC films and no solution for Ge P-channel strain has been found. It is even more challenging to realize epitaxy films for channel-last transistors with conventional epitaxial growth techniques.